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44 Cards in this Set

  • Front
  • Back
Motor unit
one motor neuron and all muscle cells that motor neuron synapses with
recruitment
change force of contraction by changing how many motor units are activated
Four things that effect force of contraction:
1. frequency of stimulation
2. length of cells at beginning of contraction
3. extent of fatigue
4. thickness of muscle fibers
Frequency of stimulation info.
-if you apply second stimulus before contraction has had chance to relax, you will cause second action potential. 2nd contraction adds to first and you get SUMMATION OF MUSCLE TWITCH.
-force of contraction is larger for each subsequent contraction
Internal tension
-tension produced by external tension-tension measured where tendon meets bone
-if frequency of action potential is high enough, maintains calcium ion concentration long enough, internal tension will equal external tension, take the stretch out of series elastic components
Length of muscle cells at beginning of contraction info.
-how much overlap between thick and thin filaments
-optimal length has maximum overlap of thick and thin myofilaments without interference
Extent of fatigue info.
-accumulation of lactic acid
-pH will decrease-pH effects enzymes
-will effect myosin cross-bridge
-depletion of ATP, cannot cycle completely
Thickness of muscle fibers info.
-over time related to how many myofibrils are in muscle cell
-thicker muscle-more myofibrils
-change by exercising, make more myofibrils
Muscle metabolism info.
Energy sources:
1. Any ATP in cytoplasm
2. Creatine phosphate+ADP
->ATP and creatine (substrate phosphorylation) enzyme creatine phosphokinase
3. Glycolysis: glucose ->
2 pyruvic acid + 2 ATP
4. Oxidative metabolism: Kreb's cycle and electron transport system
Red, slow twitch skeletal muscle:
-contract slowly-myosin
-isozymes determine-myosin isozyme is slow
-resistent to fatigue
-oxidative metabolism energy source
-have lots of mitochondria
-lots of copies of enzymes necessary
-myoglobin-carries O2 throughout muscle cell
White, fast twitch skeletal muscle:
-fast myosin isozyme
-contracts quickly
-found in arms and fingers
-fatigues easily
-use glycolysis for main source of ATP
-fewer mitochondria
-no myoglobin
-have a lot of glycogen
Intermediate, fast twitch skeletal muscle:
-intermediate in between red and white, for fatigue
-use both glycolysis and oxidative metabolism
-found in leg muscles
-intermediate amount of mitochondria, etc.
Cardiac muscle:
-have sarcomeres-basic way contract same as other muscles
-calcium ion concentration will control force of contraction
-have lots of mitochondria and myoglobin
-as long as O2 in blood, heart will not fatigue
Cardiac muscle (continued):
connected by intercalated discs:
-desmosomes (holds them together)
-gap junctions (electrical synapses)
-will synchronize movement
-some cardiac cells can spontaneously generate action potential
-action potential lasts much longer
-can only perform twitch
-if stretched, will contract harder next time
Cardiac muscle (continued):
-inputs from nervous system and hormones can change force of contraction:
-effect calcium into cell/calcium released from SR
-alter myosin ATPase activity (2nd messenger)
-alter how well calcium binds to troponin (2nd messenger)
Smooth muscle:
-has no sarcomeres
-have actin and myosin
-actin is attached to dense bodies
-there is tropomyosin, but no troponin
-myosin is not in constant position
-can contract over longer distances
-myosin is very different isozyme--extremely slow
Smooth muscle (continued):
-myosin light chain (MLC) plays regulatory role in contraction
-in excitation-contraction coupling
-very small SR
-caveolae--contain calcium
-most will come from extracellular fluid
-comes in during action potential--calcium voltage-gated channels
Types of smooth muscle:
Single unit smooth muscle
-all have gap junctions between each other
-will contract all together
-can spontaneously depolarize
-referred to as pacemaker potential or slow wave potential
-autonomic nervous system can change pacemaker potential--could make bigger or smaller
-in wall of intestines, blood vessels
Multi unit smooth muscle
-no gap junctions
-every cell has to get input from nervous system
-can individually contract
-can adjust how they contract
-found in iris, erector pili
Characteristics of smooth muscle:
neurotransmitters acting through 2nd messengers can make smooth muscles contract
-hormones and paracrines can cause smooth muscle to contract
-sometimes will contract spontaneously
-by stretching--can make contract
Steps for contraction:
1. Ca2+ concentration has to increase in cytoplasm
2. Ca2+ binds to molecule called calmodulin
3. Calmodulin activates enzyme called myosin light chain kinase
4. MLCK phosphorylate myosin light chain, which turns on ATPase of myosin.
5. Myosin can bind and pull on actin and contract
Steps for relaxation:
1. To remove Ca2+ from cytoplasm, by outside cell, back into SR, back into caveolae.
2. Calmodulin will no longer be activated
3. Take phosphates off--dephosphorylation--will make phosphatase
4. Myosin cannot interact, contraction stops, cell relaxes
Latch state:
When myosin attaches to actin and won't let go--stays contracted
Caldesmon:
regulatory protein wihch would bind to actin and actin cannot bind--inhibit actin and myosin binding
Control of Body Movements
-motor unit can be different sizes because of # of muscle cells are recruited
-recruitment controlled by size of principle of recruitment
-smaller always recruited first, then medium, then largest
-larger the motor unit, larger the cell body
-smaller are easier to bring to threshold
Reflex arc
-path that impulses take
-sensory neuron carries towards CNS, decide if response needs to be made
-this is negative feedback loop
-designed to provide very fast responses to changes
-shows how well nervous system is working
Classifications of Reflexes:
1. Spinal reflexes--only involve spinal nerves
2. Cranial reflexes--only involve brain and cranial nerves
Classification of Reflexes (continued):
3. Somatic reflexes--anywhere contraction of skeletal muscle is response
4. Autonomic (visceral) reflexes--where smooth muscle, cardiac or gland secretion is response
Classification of Reflexes (continued):
5. Simple (basic) reflexes--built in reflexes
6. Acquired (conditioned) reflexes--responses that are learned as a result of practice
Acquired reflexes:
-done all the time
-like driving car
-suppress simple reflexes
-hard to change after learned
Spinal reflexes:
-somatic reflexes--skeletal muscle
-reflex arc very similar--differ in two ways
1. number of interneurons in path
2. Whether or not they cross over and involve both sides or not
Monosynaptic reflexes
one synapse between sensory input and motor output
Polysynaptic reflexes
more than one synapse between sensory input and motor input
Ipsilateral reflexes
on same side of body, sensory input and motor input on one side
Crossed reflexes:
reflex arc goes to both sides of spinal cord and body
Reciprocal inhibition
stimulate or excite one thing, inhibit opposite thing at same time
Stretch reflex
-monosynaptic
-ipsilateral reflex
-reciprocal inhibition
Deep tendon reflex
-ipsilateral
-polysnapatic reflex
-reciprocal inhibition
Crossed extensor reflex
-polysynaptic reflex
-crossed reflex
-reciprocal inhibition
Motor control center

Brain stem
give low level constant stimulation to spinal interneurons and spinal motor neurons, bringing them closer to threshold
Basal nuclei
organizing center for motor programs--series of contractions that produce desired movement
-when damaged (stroke)-dyskinesia--inappropriate body movements
Cerebellum
-gets sensory inputs from proprioceptors (located in muscles, joints)
-vestibular (equilibrium) inputs
-outputs are inhibitory-help coordinate by correcting errors
Motor cortex
1. Primary motor cortex-frontal lobe, motor map
2. Pre-motor cortex
3. Supplementary motor area
Steps of planned voluntary motor activity:
1. Motor activity is planned in pre-motor cortex and supplementary motor area.
2. At this point, also integration of other sensory inputs and comparisons to experience.
3. Choose appropriate motor program.
4. Motor program transmitted down to basal nuclei and cerebellum.
5. Those two places organize motor program and coordinate with any other ongoing motor programs.
6. The corrected and coordinated motor program is sent up to the primary motor cortex.
7. Primary motor cortex activates appropriate descending pathways to cause the motor program to happen.